1. Field of the Invention
The present invention relates to a system and method for data routing in an ad-hoc network where optimum mobile node-to-IAP links are constantly changing. More particularly, the present invention relates to a system and method for modifying an address resolution protocol (ARP) mechanism to assign a unique media access control (MAC) address for mobile node""s IAP, such that frames addressed with this unique MAC address are routed by medium-layer routing protocols to the node""s associated IAP at the time the frame is sent.
2. Description of the Related Art
In recent years, a type of mobile communications network known as an xe2x80x9cad-hocxe2x80x9d network has been developed to address the needs of multiple mobile device communication beyond traditional infrastructure coverage. In this type of network, each user terminal (hereinafter xe2x80x9cmobile nodexe2x80x9d) is capable of operating as a base station or router for other mobile nodes within the network, thus eliminating the need for a fixed infrastructure of base stations. Accordingly, data packets being sent from a source mobile node to a destination mobile node are typically routed through a number of intermediate mobile nodes before reaching the destination mobile node. Details of an ad-hoc network are set forth in U.S. Pat. No. 5,943,322 to Mayor, the entire content of which is incorporated herein by reference.
More sophisticated ad-hoc networks are also being developed which, in addition to enabling mobile nodes to communicate with each other as in conventional ad-hoc networks, further enable the mobile nodes to access a fixed network and thus, communicate with other types of user terminals, such as those on the public switched telephone network (PSTN) and on other networks, such as the Internet. Details of these types of ad-hoc networks are described in U.S. patent application Ser. No. 09/897,790 entitled xe2x80x9cAd Hoc Peer-to-Peer Mobile Radio Access System Interfaced to the PSTN and Cellular Networksxe2x80x9d, filed on Jun. 29, 2001, in U.S. patent application Ser. No. 09/815,157 entitled xe2x80x9cTime Division Protocol for an Ad-Hoc, Peer-to-Peer Radio Network Having Coordinating Channel Access to Shared Parallel Data Channels with Separate Reservation Channelxe2x80x9d, filed on Mar. 22, 2001, and in U.S. patent application Ser. No. 09/815,164 entitled xe2x80x9cPrioritized-Routing for an Ad-Hoc, Peer-to-Peer, Mobile Radio Access Systemxe2x80x9d, filed on Mar. 22, 2001, the entire content of each being incorporated herein by reference.
Generally, all of the nodes in a wireless ad-hoc peer-to-peer network provide certain similar core services and functionality, although they can each provide different functions relating to their specific purpose and application (e.g. if they are an access point, wireless router, and so on). Therefore peer-to-peer networks distinguish themselves from infrastructure networks where one or more nodes offer a superset of the functionality of the rest of the network. Infrastructure nodes in these networks typically can handle Dynamic Host Configuration Protocol (DHCP), Address Resolution Protocol (ARP), as well as other services that depend on broadcast traffic. DHCP is defined by IETF RFC 2131 and 2132, which are incorporated herein by reference, and is used by a client node to automatically obtain network settings from a central server. These network settings include the client""s IP address, the address of Domain Name Servers (DNS), the IP address of default gateways, and many other network settings. Address resolution protocol is defined by STD 0037 and RFC 0826, which are incorporated herein by reference, and is used by a network node to map IP addresses to MAC addresses so IP traffic can be delivered to specific hardware.
These infrastructure nodes are normally discovered by broadcast traffic advertisements from their client nodes in a network, however peer-to-peer networks typically do not contain specialized infrastructure nodes. The IEEE 802.11 standard offers a peer-to-peer mode in addition to an infrastructure mode. Details of the 802.11 standards are set forth in ISO/IEC 8802-11, ANSI/IEEE 802.11 xe2x80x9cInformation Technology-Telecommunications and Information Exchange Between Systems-Local and Metropolitan Area Network Specific Requirementsxe2x80x9d, Part 11: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications, the entire contents of which being incorporated herein by reference. Also, a description of the 802.11 standard is found in a book by Bob O""Hara and Al Petrick entitled IEEE 802.11 Handbook: A Designer""s Companion, IEEE, 1999, the entire contents of which being incorporated herein by reference.
These packet-switched networks can operate across many different kinds of physical hardware by using network-layer routers, such as Internet protocol (IP) routers, with multiple hardware interfaces at junctions where the different hardware mediums must communicate. In the case of fully connected multiple-access hardware mediums, such as CSMA-CD LAN""s, where all nodes can directly communicate to all other nodes via hardware broadcasts, media converters can also be inserted into the network to operate below the network layer and pass hardware frames between two different mediums, such as with a 10base2-to-10baseT media converter. In this manner, a media converter can allow a single network-layer routing domain to span multiple hardware media.
However, in an ad-hoc networking system, all routing is done below the network layer since frames in the unified network layer sub-net may be intended for nodes within either the media, wired or wireless network. Therefore, routing methods must be adapted to cross any media junctures below the network layer. However, a media converter would not fit the need because the wireless medium is highly disconnected. That is, nodes in the wireless network may not hear frames from other nodes that are geographically or electrically distant, or occupy different data channels at the time of transmission. In certain ad-hoc networks, intelligent access points (IAP""s) are connected to bridge the wired and wireless media, as network efficiency dictates that there be many diverse access points to the wired network. Details of these requirements are described in U.S. patent application Ser. No. 09/897,790, 09/815,157 and 09/815,164, referenced above.
Because the wireless network is not fully connected, the IAP""s act as proxies rather than as media converters. Whereas a LAN media converter would hear all frames from all nodes on one medium and directly replicate them on the opposing medium, frames that must cross from the wireless medium to the wired medium in an ad-hoc network are medium-addressed directly to an access point below the network layer to ensure delivery, since the source of the frame may not be within direct transmission range of an access point. In such cases, broadcast services and address resolution protocol (ARP) are handled through special tunneling mechanisms, such as address resolution protocol. Unicast frames that must cross the media carry unicast addressing, particular to the given medium, that specifies a particular IAP.
As noted, address resolution within the ad-hoc network is difficult due to the replacement of traditional LAN components with a wireless network. Whereas in a LAN, ARP may broadcast a request packet for unknown addresses with little impact, in a wireless network such broadcasts could flood the radio network. As disclosed in U.S. Provisional Patent Application Serial No. 60/357,645 to Whitehill et al. referenced above, modifications to the use of ARP satisfies the broadcast concerns of address resolution issues within ad-hoc networks, however the mobility of nodes in the network results in a need for yet further modifications.
Node mobility poses additional problems for traditional ARP uses, as address resolutions made by ARP are generally cached. Cached address resolutions work well for wired-to-wired or wireless-to-wireless unicast communications, as it reduces the need to resolve every network packet individually. Network addresses are resolved to medium addresses once, then cached for future network packets. In a typical implementation, this cache may have an expiration timeout on the order of 20-120 minutes. Upon timeout, a given network address will be re-resolved to ensure reliable resolution for situations where network addresses of given nodes change periodically, such as the case with a DHCP-managed network. When a wireless node resolves network addresses of devices on the wired medium, a medium address is determined that correlates to the node""s associated IAP and which is presumed to be the xe2x80x9cbestxe2x80x9d media bridge for the node to use. The best IAP may be selected based on bandwidth, spectral efficiency, or other reasons specific to the network. To provide this functionality, the ARP mechanism is implemented in such a way as to offer the medium address of a node""s associated IAP when resolving network addresses of wired nodes. However, given node mobility, the best IAP may not be static for a given mobile node. In such a network, IAP associations may be formed and broken at a higher rate than the ARP expiration timeout would correct for. While the wireless network might allow routing to less-appropriate IAP""s, the network would not operate very efficiently. Furthermore, security issues might not allow a non-associated IAP to proxy for a given wireless node.
Accordingly, a need exists for a system and method for modifying the ARP mechanism to assign a medium address for a mobile node""s associated IAP in which the optimum IAP is targeted.
An object of the present invention is to provide a mechanism for trans-medium address resolution on a network with at least one highly disconnected medium having multiple access points to other media.
Another object of the present invention is to provide a system and method for modifying the ARP mechanism to assign a medium address for a mobile node""s associated IAP which directs medium-layer routing protocols to route medium frames so addressed to the node""s associated IAP at the time the frame is sent.
These and other objects are substantially achieved by providing a system and method for identifying optimum IAP addresses which are subject to change at rates greater than traditional address updating may provide for. Once identified, the system and method provides a xe2x80x9cuniquexe2x80x9d media access control (MAC) address in address resolution protocol (ARP) when wireless nodes are communicating with nodes on a core LAN. Medium layer routing protocols recognize that medium frames addressed with this unique address should be routed to the node""s currently associated IAP, whichever IAP that might be at the moment the frame is sent.